Try deleting the old version first.
There is also a tutorial on installing firefox in the tutorial section.
how can i update firefox from 3.0.11 to the new one and not have both on the system??
when i downloaded it i managed to open the knew one from th terminal but every time i open it from the k menu or the panel the old one pops up!!
even when i click on help from firefox menu bar, the check for updates is not available witch is weird!!